Another salient point is that we almost never take into account the fact that we accommodate to the conditions around us. We truly believe that if we win the lottery we will be happy forever, even in the face of mountains of data to the contrary.
The most surprising result, I thought, was that (in the late 1990s U.S. dollars) happiness begins at $40k per year, and increases only slightly for incomes up to $100k per year, and then is essentially flat. One of the drivers for this was that, at $40k per year, you typically get health insurance through work, and this removes the primary worry that brings people's happiness down.
I think the really interesting thing would be to see if you could convince rich people of this so that they voluntarily, without legal compulsion, would give up some of their wealth to make others happy. I'd be interested to see if I would do this, if I ever became a .com/web 2.0 zillionaire.